I am not sure whether what this method could be, nmap won't do so quickly, it is made to handle a lot, All i can share is people keep looking for it, I once left squid open with nu password, and within 2-3 days i had like 200 GB or more data transfer. Well, it was a new IP, and new server, so I think people keep on scanning that, its easy that you ll end up being on internet forums if you leave such services on.